1. Field of the Invention
The present invention relates to a novel organosilicon compound having a β-ketoester structure within the molecule, and a pressure-sensitive adhesive composition for a liquid crystal display device that uses the organosilicon compound as an adhesive improver, or more specifically, a pressure-sensitive adhesive composition for a liquid crystal element that can be detached during production of the liquid crystal display device, but develops increased adhesion over time, and exhibits excellent durability when used under conditions of high temperature and high humidity.
2. Description of the Prior Art
Organosilicon compounds having a β-ketoester structure within the molecule and also containing an alkoxysilyl group within the molecule are already known, and are disclosed, for example, in Patent Reference 1. These compounds are used as metal ion scavengers, surface treatment agents for inorganic materials, interfacial binding agents for composite materials composed of an inorganic material and an organic material, dispersants for inorganic materials, and adhesion improvers for improving the bonding of organic-based adhesives to inorganic substrates. They are also useful as adhesion improvers for primer compositions.
In this manner, β-ketoester structure-containing organosilicon compounds are already in use within organic-inorganic composite materials and organic resin-based adhesives. However, when a conventional β-ketoester structure-containing organosilicon compound is added to a resin or rubber, and is subsequently mixed with an inorganic material such as an inorganic powder like silica, alumina or mica that is added as a filler, the effects of the organosilicon compound in improving the interfacial binding and the dispersion are not entirely satisfactory. Furthermore, when a conventional β-ketoester structure-containing organosilicon compound is added as an adhesion improver to an organic adhesive such as an epoxy-based or urethane-based adhesive, the improvement in adhesion is not entirely satisfactory.
A liquid crystal element is formed from two glass substrates having a transparent electrode on the surface of the glass that contacts the liquid crystal, a liquid crystal material that is used to fill the space between the two glass substrates, and either a polarizing plate, or a laminate composed of a polarizing plate and a retardation plate, disposed on the outside surface of each of the two glass substrates.
In this type of liquid crystal element, each polarizing plate or laminate composed of a polarizing plate and a retardation plate is bonded to the surface of the glass substrate using an acrylic resin-based pressure-sensitive adhesive.
In a production process for a liquid crystal element that uses this type of pressure-sensitive adhesive, if a problem arises during the bonding of the polarizing plate or the laminate composed of a polarizing plate and a retardation plate to the glass substrate, then provided the polarizing plate or the laminate composed of a polarizing plate and a retardation plate is able to be detached from the glass substrate, and a new polarizing plate or laminate composed of a polarizing plate and a retardation plate then re-bonded to the glass substrate, the expensive liquid crystal material and the cell containing the liquid crystal material need not be discarded, and can still be used to produce a liquid crystal element having favorable liquid crystal performance. From this perspective, the pressure-sensitive adhesive is preferably able to be readily released if a problem occurs during the bonding of the polarizing plate, or the laminate composed of a polarizing plate and a retardation plate, to the glass substrate.
In recent years, the range of potential applications for liquid crystal elements has expanded enormously, and includes displays for personal computers, vehicle-mounted liquid crystal monitors, and televisions. As this range of potential applications expands, the environmental conditions in which the liquid crystal elements are used are becoming increasingly severe. Accordingly, the adhesive strength between the polarizing plate, or the laminate composed of a polarizing plate and a retardation plate, and the glass substrate is preferably as strong as possible in order to withstand these environmental conditions, and it is desirable that this superior adhesive strength is maintained over long periods without fluctuation.
The pressure-sensitive adhesive used in bonding the polarizing plates, or the laminates composed of a polarizing plate and a retardation plate, to the glass substrates of the liquid crystal element requires somewhat contradictory properties, in that when a problem occurs during the production process and an attempt is made to detach a polarizing plate or a laminate composed of a polarizing plate and a retardation plate, the polarizing plate or laminate composed of a polarizing plate and a retardation plate should be readily detachable from the substrate without damaging the liquid crystal element, but in contrast, once the liquid crystal element has been supplied for actual use within a practical application, stable adhesive strength should be maintained over a long period.
Conventionally, acrylic resin-based pressure-sensitive adhesives that use an organosilicon compound having a β-ketoester structure within the molecule as an adhesion improver have been reported, for example in Patent Reference 2, as enabling ready detachment from the substrate of the polarizing plate or laminate composed of a polarizing plate and a retardation plate without damaging the liquid crystal element if a problem occurs during the production process, and yet yielding stable adhesive strength that can be maintained over a long period once the liquid crystal element has been supplied for actual use within a practical application. However, even if these known organosilicon compounds having a β-ketoester structure are used, the stability of the adhesive strength over a long period is still unsatisfactory under some of the severe operating conditions now being required, meaning further improvement is required.
[Patent Reference 1] U.S. Pat. No. 4,981,986
[Patent Reference 2] JP 3,533,446 B2